Mirroring and replication of electronic data between two or more disk subsystems is a common method used in prior art to increase the availability of disk storage where business continuity is required.
FIG. 1 illustrates prior art architecture of such system.
A host computer 10 hosts a plurality of business applications 12A, 12B, 12C which should be able to be operated continuously in order to avoid business-critical situations. In order to provide computing resource redundancy, a standby host computer 14 is provided at a failover site which takes the job of host computer 10, if ever this computer's continuous operation should fail.
Common setups in prior art require two or more independent disk arrays 16, 17 respectively. One primary disk area 18 stores all data and is used as the primary storage device. A mirroring or remote copy facility 13 allows synchronizing the data being stored on the primary disk area with the same data being stored on the other secondary, tertiary, etc., disk areas. Asynchronous or synchronous writes are chosen depending on the related recovery point objective abbreviated as RPO in prior art.
The applications 12 storing their data on the primary disk array are notified that the data is written. If the mirroring is carried out asynchronously, the application 12 get notified when the data is stored on the primary disk array. Synchronous writes ensure that the data is also written to disk in the mirror device. A disaster recovery solution based on such architecture requires a redundancy of at least 100% of disk storage so that a “hot device” (i.e., a permanently used primary device) has at least one associated standby device with the same storage capacity.
With the increase of costs for the power consumption required for the disk drives the total cost of ownership (TCO) increases significantly. A typical disk drive in idle mode consumes 6-8.5 Watt increasing up to 9-14 Watt in the case of performing various seeks of the hard disk heads. This is disclosed in “HDD Diet: Power Consumption and Heat Dissipation” by Alex Karabuto (1x@ixbt.com) published Jul. 11, 2005 on the world wide web at digit-life.com/articles2/storage/hddpower.html.
Statistics show that about 27% of the cost for power consumption in IT centers is derived from disk storage. Approaches are already taken in prior art to reduce the power consumption. Introducing pre-stage storage means together with algorithms aware of disk devices and their usage allows reducing the power consumption based on the fact that idle hard disks use less power. This is disclosed in “Reducing Energy Consumption of Disk Storage Using Power-Aware Pre-stage storage means Management” by Qingbo Zhu and Yuanyuan Zhou, Department of Computer Science, UIUC and published on the web at research.ibm.com/aceed/2005/posters/zhu-abstract.pdf.
Another prior art approach changes the rotational speed of the disks itself so that idle hard disks run slower. This is disclosed in “Reducing Disk Power Consumption in Servers using DRPM” by Sudhanva Gurumurthi et al., published on the web at cs.virginia.edu/˜gurumurthi/papers/ieee_comp03.pdf.
Other utilities like idle-timeouts for powering down hard disks in workstations or laptops are common practice of prior art.
So, although some investigations and proposals are known in prior art for a general saving of power consumption when operation a hard disk, there is no method known in prior art how to save power in business-critical mirroring storage subsystems. Here, the primary and general policy is to keep the business data safe and accepting a high power consumption of such mirroring systems as unavoidable.